I need help to find a plan for a elapse time timer. The kind that will tell the time from one input and the second.?

I am setting up a race course for gravity racer.  You can not see the top or start from the bottom.  An electric clock will stop some of the arguments.  Thank you

Some shameless self promotion of my own instructables, but it sounds like it would apply well to your application.

I created an instructable for a chonograph used with an air cannon. It starts a timer when one switch is tripped and stops the timer when a second switch is tripped. A box with a character LCD is used to display the elapsed time between the switches being tripped, in microseconds. The software for the microcontroller used can time events from microseconds up to 16 seconds in duration.

Any kind of switches that change from closed to open when tripped can be used. Check out the instructables under my profile.
rickharris6 years ago
You will need a light gate and some kind of accurate timing system. depending on your skill set this is a job for a microcontroller or lap top.